1. Field of the Invention
The invention relates to an indentation in a plastically deformable material.
2. Discussion of the Prior Art
French reference FR 2 482 484 discloses an indentation in the form of a bead in a pipe body, which has an essentially rectangular cross section. Beads of this type can have only a relatively slight depth, since otherwise cracks would occur.
German references DE 20 20 868 and DE-PS 69 305 describe methods which can be used to produce an indentation of relatively great depth which has a curved base to the indentation. The base of the indentation is of semicircular design, as a result of which the width of the indentation turns out to be relatively large.
In some applications, however, the indentation must have a great depth in conjunction with a slight width. An example of this is known from German reference DE 42 36 961, in which an indentation is part of a fire protection means for a vibration damper. The required depth of the indentation is also determined by the wall thickness of the piston ring of the vibration damper. It must be ensured that the indentation can come to bear against the top side of the piston. Particularly in the case of injected or laminated piston rings such as are known from German reference DE 195 01 792, an indentation must be rings such as are known from German reference DE 195 01 792, an indentation must be particularly deep, but also narrow, since the width of the indentation is to be regarded as lost length for the stroke of the vibration damper.